Engine/Transmission (1998.5 - 2002) When engine returns to idle, it surges

[HD-J78]

Ok all you smart people out there

I Replaced the VP44 and lift pump, and also the two sensors on the intake manifold, at the rear.

After all was done, engine seems to perform better BUT!!!!

Now when the engine comes down to idle, like while shifting if taking too long or idle at red light or any other time, the idle goes down to it's normal idle speed the surges up about 100-200rmp about 3 or 4 times then settles down again at idle. So I did the voltage check of the APPS and as far as I can tell I get a smooth voltage increase and decrease at full travel. Then I drove it still plugged in and the voltage stayed constant while the engine did the surging. So, I kind of doubt that the APPS is the culprit.

I got new seals for the fuel inlet line and the fuel return line at the pump, and replaced the rubber fuel hose that joins the hard lines from the fuel filter to the pump inlet.

Any ideas?



2000 4x4 5 speed



Thanks.

 

[Alan Reagan]

I'm assuming that it is not a rough idle, just an idle speed increase.



I would try two things.



First, lube your throttle cable. Don't laugh. Sometimes there is enough "stickion" to cause it to put tension on the TPS causing the idle speed to increase.



Second, calibrate the TPS. If I remember correctly, turn the key on, slowly press the accelerator all the way to the floor and then slowly release it to the idle position. Turn the key off.

 

[HD-J78]

I guess you could call it a idle like a "hot" cam, kind of like some Harleys' idle? It drops to idle just fine, then goes up and down for about 3 or 4 cycles relatively fast, then settles down at normal idle.
Does the coolant temp probe have any part in the ECM telling the pump what to do?

 

[cerberusiam]

What IP did you use in the replacement? Some of these remans have a lopey idle out of the box, and, do you have bigger injectors or other mods?



Definitely try the APPS reset to make sure there is not a mismatch between the APPS and new pump.

 

[SHobbs]

Mine used to bounce a little when I came to a stop. Similar to what you are describing, drop to idle and surge a couple times. Not sure which was the culprit but, I changed the cam position and crankshaft position sensors and it stopped the bouncing.

 

[HD-J78]

I got the pump from Blue Chip Performance, the stock replacement one. I've done the APPS reset numerous times, makes no difference. It seems to only do it once the temp gets at or above about 150 degrees. I drive around with volt meter hooked up to APPS for a few days now and it does not show any volt increase or fuel pressure increase during the surging.
Gonna try the air bubble check and also "hot wire" the VP44 to see if it runs like it's suppose, though I really don't think this will prove anything since I can't duplicate the scenario this way.

 

[HD-J78]

Ok, did the "hot wire" the pump thing and it started and idled just fine. I did note that it idles about 100rpm lower than when the wiring harness is plugged in, don't know it this is normal or not. Then did the clear tube thing and did not notice any bubbles at any time.
Might be time to replace all of the sensors on the block?

 

[HD-J78]

Drove it around yesterday after these tests and the idle surge was gone? Then drove it around today again and the idle surge was still gone? What are these suppose to idle at? It idles at about 750rpm.

 

[Road Dog]

I checked the idle with my Edge Juice -- 800rpm exactly at normal operating temperature.